Engines emit exhaust gas that includes carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx). An exhaust treatment system reduces the levels of CO, HC, and NO in the exhaust gas. The exhaust treatment system may include an oxidation catalyst (OC) (e.g., a diesel OC), a particulate filter (PF) (e.g., a diesel PF), and a selective catalytic reduction (SCR) system. The OC oxidizes CO and HC to form carbon dioxide and water. The PF includes a PF substrate that traps particulate matter from the exhaust gas. The SCR system typically includes an SCR device that reduces NOx.
Catalyst washcoats have been traditionally used with SCR devices. The washcoat chemically interacts with the ammonia (NH3) introduced to the exhaust gas, and reduces the level of NOx. Recently, catalyzed washcoats have also been applied to the PF substrate included in the PF.